According to the Levitical text, the characteristic features of leprosy were: (1) bright white spots or patches on the skin the hair on which also was white; (2) the depression of the patches below the level of the surrounding skin; (3) the existence of "quick raw flesh"; (4) the spreading of the scab or scall.

There are two forms of modern leprosy—the tubercular, or nodular, and the anesthetic, or nervous; generally both forms are present. The nodular form begins, as a rule, as round or irregularly shaped spots, commonly of a mahogany or sepia color. These often disappear, and are followed by the appearance of nodules. In an advanced stage the face is covered with firm, livid, nodular elevations: the nose, lips, and ears are swollen beyond their natural size, the eyelashes and eyebrows are lost, and the eyes are staring; the whole producing a hideous disfigurement. As the disease progresses, insensibility of the skin and paralysis ensue, and the fingers and toes may rot away.

In the Biblical description, one is immediately impressed by the absence of all allusion to the hideous facial deformity, the loss of feeling, and the rotting of the members. If such conspicuous manifestations had existed they could not possibly have escaped observation. The Levitical code prescribed that the several examinations of the person suspected should be made at intervals of seven days, thus enabling the priest to note the progress of the disease. Leprosy is an exceedingly slow disease, particularly in the beginning, and a fortnight would show absolutely no change in the vast majority of cases. Moreover, the "lepra Hebræorum" was a curable disease. When the leper was cured the priest made an atonement before the Lord, and expiatory sacrifices in the form of a sin-offering and a trespass-offering were made also. Modern leprosy is, except in isolated instances, incurable.

The probabilities are that "ẓara'at" comprised a number of diseases of the skin, which, owing to the undeveloped state of medical science at that period, were not distinguished. The white spots, upon which so much diagnostic stress was laid, were in all likelihood those of vitiligo, a disease quite common in tropical countries, and characterized by bright white spots, the hairs on which also become white. Vitiligo begins as small patches, which slowly spread, often involving ultimately large areas of the body's surface. The disease is harmless, but most disfiguring in those of swarthy complexion.

In the Septuagint "ẓara'at" is translated by "lepra." It is reasonable to assume that the Hebrews attached the same meaning to "ẓara'at" that the Greeks did to "lepra," which is derived from "lepros" (= "rough" or "scaly"). According to the medical writings of Ægineta, Ætius, Actuarius, Oribasus, and others, lepra was uniformly regarded as a circular, superficial, scaly eruption of the skin; in other words, their lepra was the psoriasis of modern times. There is absolutely nothing in the Greek description of lepra that suggests even in a remote manner the modern leprosy. The Greeks, in speaking of true leprosy, did not use the term "lepra," but "elephantiasis." It is evident, therefore, that they meant by "lepra" an affection distinct and apart from the disease of leprosy as now known. The confusion and obscurity that have enveloped this subject for centuries have resulted from the use of different terms in successive ages to designate the same disease, and from the total change in the meaning and application of the word "lepra."

There is much reason to believe that the segregation of lepers was regarded, at any rate at certain periods, more in the light of a religious ceremonial than as a hygienic restriction. Ẓara'at was looked upon as a disease inflicted by God upon those who transgressed His laws, a divine visitation for evil thoughts and evil deeds. Every leper mentioned in the Old Testament was afflicted because of some transgression. "Miriam uttered disrespectful words against God's chosen servant Moses, and, therefore, was she smitten with leprosy. Joab, with his family and descendants, was cursed by David for having treacherously murdered his great rival Abner. Gehazi provoked the anger of Elisha by his mean covetousness, calculated to bring the name of Israel into disrepute among the heathen. King . . . Uzziah was smitten with incurable leprosy for his alleged usurpation of priestly privileges in burning incense on the golden altar of the Temple" (Kalisch). It would have been quite natural for the people by a posteriori reasoning to have regarded persons afflicted with ẓara'at as transgressors; they had violated the laws of God and their transgressions had been great, else they would not have been so afflicted.

Writers who hold the view that the exclusion of lepers had chiefly a religious significance conclude from these facts that lepers were obliged to remain outside the camp because they were regarded as likely to morally infect others. As long as the signs of the disease remained upon them they were obliged to live outside the camp. It is reasonable to believe that, although Biblical and modern leprosy are, in all probability, not the same disease, thepresent custom of segregating lepers had its origin and stimulus in the Biblical example of segregating those afflicted with ẓara'at. Had the Bible never been written it is probable that lepers would to-day be permitted to go in and out among their fellows unhindered, for leprosy is a much less actively communicable disease than several other well-known affections in the case of which segregation is not practicable.

The Biblical description of leprosy of garments and houses is strikingly analogous in its wording to that of leprosy of persons. The passages in Leviticus (xiii. 47-59) are at present inexplicable in the light of modern science. The probabilities are that the description refers to stains upon garments produced by pus and blood from boils and ulcers of various kinds. Thus alone could the greenish and reddish stains be accounted for. That the description in Lev. xiv. 33-48 could not have applied to a leprosy of walls of houses is beyond reasonable doubt: such conceptions may possibly be ascribed to Oriental fancy and love of metaphor. Chemical incrustations and mildew were doubtless in this manner endowed with the symptoms of a living and spreading disease.

The subject of leprosy is treated chiefly in the treatise Nega'im. The Talmud maintains that Lev. xiii. 1 et seq. refers generally to any disease that produces sores and eruptions on the skin (Sifra 60a). The following epitomizes the Talmudic treatment of leprosy:

1. Leprosy was not considered contagious. While all peoples of antiquity, from earliest times up to some centuries after the Talmudic period, held (as at the present day; Katzenelenson, in "Ha-Yeḳeb," p. 75, St. Petersburg, 1894) that leprosy was contagious, the Talmudic writers treated it as not contagious. The following evidences this: (1) The Mishnah does not consider a leprous pagan or an unnaturalized proselyte ("ger toshab") ritually unclean (Neg. iii. 1, xi. 1). (2) If a bridegroom, on his weddingday, observes symptoms of leprosy on his skin, he is not required to submit himself for examination at once, but he may postpone it until the seven days of his nuptials are over. Similarly, one who is affected with it during the holy days may postpone examination until they are over (Neg. iii. 2). Under other circumstances, one afflicted with leprosy is forbidden intercourse with his wife (Ḥul. 141a). (3) The Mishnah says that doubtful cases (with two exceptions) are not to be considered unclean (Ḥul. 9b et seq.). (4) The Bible commands that if the priest finds white hair on the parts affected he shall declare the subject unclean, for the white hair is a certain symptom of leprosy. But the Mishnah says that if the hair is plucked out before the examination takes place the person is clean (Neg. viii. 4). It was not, then, fear of contagion that led to regarding the leper as unclean.

2. Talmudic tradition, basing its definitions on the etymology of the Biblical terms used, knows of four different degrees of white in cases of leprosy, but not of "neteḳ." (Lev. xiii. 30). "Baheret" is of the whiteness of snow; the second degree recognized is of the whiteness of lime; "se'et" is of the color of the white of an egg; and the next degree of whiteness is that of white wool. The Mishnah adds, also, some intermediate shades; but it calls "bahaḳ" all those beyond the four shades in question (Neg. i. 1-3).

3. While the Bible divides the disease into "white leprosy" and "ulcerous leprosy" ("miḥyah"), the Mishnah divides it into "limited" ("ḳeṭannah") and "extended" ("gedolah") leprosy (Neg. viii. 9). Accordingly it expounds Lev. xiii. 9-11 as referring to "limited" leprosy, and Lev. xiii. 12 et seq. as applying to "limited" leprosy which has extended, and as such has become clean.Leprosy if "extended" at the outset is to be treated as limited leprosy (Neg. viii. 7); extension does not render leprosy clean, unless following upon a disease which has shown sure symptoms of real leprosy (Neg. viii. 3). Leprosy should, moreover, be considered extended only when it invades the face (Neg. x. 9) and, if the individual is bald and beardless, the scalp and chin (Neg. vi. 8, viii. 5). If, after the scales of leprosy have spread over nearly the whole body, a bleeding and scaleless ulcer (miḥyah) is observed, the subject is unclean. Similarly, if the scales, having covered almost the whole body, fall off in one place and uncover an old bleeding ulcer, the subject is unclean (Neg. viii. 2).The bleeding ulcer must be of the size of a lentil in order to render one unclean, in cases both of "limited" and of "extended" leprosy. In case the ulcer develops on the extremities of the body, as on the fingers or toes, or on the ears, nose, breast, etc., the person is not considered unclean (Neg. vi. 7). But if this ulcer had once been covered with scales and had then become open again, the person is unclean, unless the remaining scales are smaller than a "gruel" ("geris"; Neg. viii. 1). Finally, the miḥyah does not make a person unclean if it invades a place previously affected by a "sheḥin" or a burn, or if it develops on the hairy parts of the body, or in the recesses and cavities (Neg. vi. 8). When it settles on parts from which the hair has fallen out, or on parts previously affected by sheḥin or a burn, but which have become entirely healed before the appearance of the leprosy, two cases are to be distinguished, according as the miḥyah has previously been covered with scales or not; in the latter case it does not render the subject unclean.

4. In regard to leprosy consequent upon sheḥin or a burn (Lev. xiii. 18-28), the Mishnah maintains: (1) If the sheḥin or the burn has not been healed before the appearance of the scales of leprosy, the person is clean (Neg. ix. 2). (2) Where these affections have become completely healed before the appearance of leprosy, only that is to be considered as leprosy which invades parts of the body never before diseased (ib.). (3) Finally, leprosy consequent upon sheḥin or a burn is not rendered unclean by the development of a miḥyah, and one so affected can be isolated for seven days once only, not twice, as in the case of an ordinary leper (Neg. iii. 4).

5. In regard to leprosy on the scalp and chin (Lev. xiii. 29 et seq.), the Mishnah contains the following:(1) The symptoms of leprosy here (i.e., leprous scales) may present any color; but in any other part of the body only one or more of the four degrees of white can be presented (Sifra 60a). (2) As the Mishnah distinguishes a "limited" and an "extended" leprosy, so it distinguishes a "limited" and an "extended" neteḳ (Neg. x. 9). (3) The neteḳ does not become unclean in consequence of the presence of a miḥyah, but through the presence of fine white or yellow hair, and through the extension of the disease ("pisyon"; Neg. x. 1). (4) Finally, if the hair of the head or of the chin has fallen out, those parts are to be treated like other parts of the body (Neg. x. 10).In the Talmud the classification or definition of leprosy and of its symptoms seems to be determined not by medical ideas, but by a literal and indiscriminating adherence to the letter of the Levitical law; Talmudic sages were satisfied merely with communicating the Biblical decisions. The Rabbis appear at times even to confuse true leprosy with eczema.

Leprosy among Jews is seldom mentioned in modern medical literature. Zombacco ("Bul. de la Société d'Anthropologie de Paris," Oct., 1891) states that the disease is very frequent among the Jews of Constantinople. Buschan, quoting this statement ("Globus," lxvii. 61), argues that the predisposition of the Jews to leprosy is a racial characteristic hereditarily transmitted from the ancient Hebrews to the modern Israelites. In support of this he mentions that the Karaites of Constantinople have not been observed by Zombacco, during his twenty years of medical practise among them, to suffer from leprosy. These Jews Buschan considers Jews only by religion, not by virtue of blood-relationship to the Semites. Ethnically he considers them as derived from the Chazars and other peoples of "Finnic" blood. On the other hand, the Rabbinic Jews of Constantinople, who are derived from "Syro-Arabic Semitic" race, have been often observed by Zombacco to suffer from the disease. He further states that the Mohammedans, Christians, Greeks, Armenians, and other non-Jews in Constantinople are free from it, notwithstanding the fact that they come in contact with the Jews. All this tends to show that the alleged predisposition of the Jews to leprosy is an ethnic trait.

This allegation, based as it is on very scanty evidence, is not confirmed by any other observer. In Russia, where in some provinces leprosy is endemic, the Jews are not observed to be frequently affected, while in some Oriental countries the evidence available tends to show that, on the contrary, the Jews are peculiarly free from leprosy. Thus, Nicholas Senn, speaking of leprosy in Jerusalem, says: "Most of the lepers are Arabs; and the Jews are singularly free from this disease. . . . Among the 47 inmates [of the Jesus Hilfe Hospital] there is only one Jew. Dr. Einsler, during his long and extensive practise in Jerusalem, has seen only five Jews affected with leprosy; and of these one came from Salonica and of the remainder two from Morocco. It seems that the Jerusalem Jews have in the course of time acquired an immunity from this disease, notwithstanding the increase of poverty and unsanitary surroundings" (N. Senn, "The Hospitals in Jerusalem," in "American Medicine," iv. 509-512).